What if we used a signal which only had a zero to + (or -), repeated for awhile. Like a pulse. There is an average level that is + or an equivalent dc level. What does this do to the circuit...

Well...if it is a symmetrical amp, DC coupled, we can believe one side of the power stage will heat more and the other refresh ?
Offset can increase, or decrease...depending how it was ? or the level ? Or the one after the other ?
Distortion can increase slightly, or decrease, depending how the parts mismatch ?
Of course, the thermal inertia is slow enough for any servo can correct this DC (because your signal is a symmetrical signal with a DC equal to half its peak to peak value) before it become important, while the power units are thermally coupled with the radiator ?

But the main question i ask to myself is: What kind of instrument would produce such a signal ? Even Kick drums, with its first attack always in the same sens is globally near symmetrical, main dis-symmetry on half a period...
I noticed that kick drums can sound a little different, switching their phase, but i believe it is due to loudspeakers, as i never noticed impact on other instruments.playing in the same time.
Did i miss something ?

Well...if it is a symmetrical amp, DC coupled, we can believe one side of the power stage will heat more and the other refresh ?
Offset can increase, or decrease...depending how it was ? or the level ? Or the one after the other ?
Distortion can increase slightly, or decrease, depending how the parts mismatch ?

Too broad... maybe this, maybe that. (many SE and other audiophile circuits are not symmetrical). Looking for numbers... after-all I am looking at .001 and less thd numbers for SOTA circuits. Looking for CMRR of at least -100 db.
It may not take very much asymmetry in waveforms to cause increase in distortion.... for some circuit topologies. Assume 1k-10K source Z for worst case. Also, for worse case, assume C/L gain is on the low side. Thx - RNM

Fiber-Optic microphones: If you shine a light on a vibrating diaphram and pick up the reflected light via a f.o. to a detector.... you pretty much dont have to worry about noise, amps and Z and cable pick up of hum emi/rfi et al. Why arent more using them and developing them further for more recording appl? Why, why, why? -RNM

Fiber-Optic microphones: If you shine a light on a vibrating diaphram and pick up the reflected light via a f.o. to a detector.... you pretty much dont have to worry about noise, amps and Z and cable pick up of hum emi/rfi et al. Why arent more using them and developing them further for more recording appl? -RNM

Not asking for you to take my word for it. But without details, falling back on photonics as if it were some sort of panacea is naive. And when one adds the realistic details, it becomes much more pessimistic, most of the time.